1. Field of the Invention
The present invention relates to a grip heater control apparatus, and more particularly to a grip heater control apparatus for controlling a grip heater incorporated in a steering handle of a motorcycle, a snowmobile, a personal water craft, a three-wheeled buggy, or the like.
2. Description of the Related Art
Heretofore, there has been employed a grip heater control apparatus for controlling electricity supplied from a battery to a heater which is provided in a handle grip (also called a steering grip, hereinafter referred to as “grip”) of a steering handle of a motorcycle, a snowmobile, a personal water craft, a three-wheeled buggy, or the like, thereby to heat and keep the grip at a suitable temperature to provide a comfortable driving environment for the driver to drive the vehicle in winter or cold climate.
The grip heater control apparatus generally comprises a Nichrome wire or a film-like board, which functions as a heater, wound circumferentially in the grip that is made of rubber or the like, a cylindrical potentiometer having a function as a switch and a function to adjust the temperature of the heater, a controller integrally combined with the potentiometer for controlling electricity supplied to the heater, and a wiring that interconnects the heater and the controller. The potentiometer and the controller are fixed integrally together in a position near the grip by a stay or the like.
When the potentiometer is turned clockwise from its initial position, the grip heater control apparatus is energized to supply an amount of electricity depending on the angular displacement of the potentiometer from the battery through the controller and a lead to the Nichrome wire. When the potentiometer is turned further clockwise, the amount of electricity supplied from the battery to the Nichrome wire is controlled in proportion to the angular displacement of the potentiometer. The supplied electricity causes the Nichrome wire in the grip to generate heat, heating the grip to a certain temperature. The temperature of the grip can freely be adjusted through the heater by turning the potentiometer.
Conventional grip heater control apparatus are disclosed in Japanese laid-open patent publication No. 10-79284 and Japanese patent No. 3231247, for example.
In the grip heater control apparatus disclosed in the above publications, in order to adjust the electricity supplied to the heater by operating the potentiometer that is integrally coupled to a power supply switch, the output voltage from the potentiometer is compared as a comparison voltage with a predetermined periodic voltage wave, e.g., a triangular voltage wave in level to produce a PWM output signal. The PWM output signal is applied to turn on and off a switching circuit to control the electricity supplied from the battery to the heater for thereby heating the heater.
The grip heater control process is ancillary to the vehicle and when the voltage of the battery drops below a minimum voltage required to energize the starter motor of the vehicle, the supply of the electricity from the battery to the heater needs to be stopped in order to give priority to the propulsion of the vehicle. The vehicle has a battery voltage monitoring circuit for forcibly turning off the switching circuit regardless of the value of the comparison voltage if the battery voltage which is detected becomes close to the minimum voltage required to energize the starter motor. The vehicle also has a failsafe circuit for forcibly turning off the switching circuit if the comparison voltage is not determined.
The battery voltage monitoring circuit controls the switching circuit to inhibit energization of the heater if a voltage value based on the battery voltage supplied to the battery voltage monitoring circuit is lower than a first voltage threshold VS1, and controls the switching circuit to allow energization of the heater if the voltage value based on the battery voltage supplied to the battery voltage monitoring circuit is higher than a second voltage threshold VS2 (VS2>VS1).
If the minimum voltage value required by the battery is represented by VN, a voltage drop caused by the resistance of the wiring between the battery and the battery voltage monitoring circuit is represented by Δv1, and a maximum detected error voltage expected by the battery voltage monitoring circuit is represented by Δv2, then the first voltage threshold VS1 is set to VS1=VN−Δv1+Δv2, providing a hysteresis based on the first voltage threshold VS1 and the second voltage threshold VS2. When the battery voltage drops below the first voltage threshold VS1, the switching circuit is controlled to inhibit energization of the heater, and when the battery voltage rises to or beyond the second voltage threshold VS2, the switching circuit is controlled to allow energization of the heater. Thus, the switching circuit is prevented from repeatedly inhibiting and allowing energization of the heater frequently, and the minimum battery voltage is maintained. The conventional grip heater control apparatus has various drawbacks which will be described below.
The potentiometer for adjusting the temperature of the heater is expensive. Since the potentiometer has mechanically movable components such as a movable contact, the durability of the potentiometer is lowered by usage over a long period of time due to a mechanically sliding action of the potentiometer which is repeated each time the heater temperature is adjusted.
The potentiometer for instructing the controller to adjust the electricity supplied to the heater does not provide tactile clicks, and hence prevents the driver from easily recognizing adjustment instructions that the driver has made.
When the battery voltage is initially applied as when the engine of the vehicle is started, the battery voltage is unstable because of strong voltage variations of the alternator, causing light-emitting diodes (LEDs) to emit repeated flickering light that tends to make the driver feel uneasy.
When noise is added to the detected battery voltage, no accurate battery voltage can be obtained. Consequently, it is necessary to set a minimum required battery voltage with a margin in view of possibly added noise. As a result, the battery voltage cannot effectively be utilized.